He was climbing to reach the ball when the roof of the building gave way and the boy crashed to the ground below, landing in a tank containing a chemical once used to strip furniture.

The youngster was initially taken to Rotherham District General Hospital before being transferred to the burns unit at Sheffield Children’s Hospital, where his condition was stable, South Yorkshire Police said.

Caustic soda, also known as sodium hydroxide, can cause severe burns, scarring and blindness.

Adrian Podmore (27), who lives across the road from the derelict workshop on Bear Tree Street, said the boy looked as though he was covered in blood.

He said: “He was screaming to a woman ‘help me, help me’.

“I thought he’d been hit by a car or something like that because he was screaming in pain, but I talked to one of the kids who said he’s actually fallen into some acid.

“It looked like he had blood all down his face.” Railway worker Mr Podmore said there were no warning signs about the building and neither of its two entrances were secured at the time of the accident.

“A guy came the following day and boarded it all up and secured it,” he added.

Mr Podmore said children always played football in the area.

“They’re really good kids, not naughty or anything like that,” he said.

Last night, there was little evidence of the accident, which happened at 5.45pm on Tuesday.

The car park behind the red-brick building was deserted and a sign mounted on a crumbling wall warned that the area was private property.

Barbed wire could be seen along the edge of the corrugated steel roof above a wooden gateway.

The boy’s mother said she and her husband rushed to the scene after one of his friends told them about the accident.

Tracey Briggs told BBC Radio Sheffield: “One of his friends came up to our house and knocked on the door, screaming that Brooklyn had dropped into some acid.

“My husband Gary ran down the street (and) I got in the car and drove down.

“As I got there he was in Gary’s arms just screaming ‘help me daddy, help me daddy, please help me’.”

The accident is now being investigated by the Health and Safety Executive with assistance from police.